1. Field of the Invention
The present invention pertains to a sensor arrangement for an anemometer using a film type precision resistor and a planar, elongated film type heating resistor supplied with an adjustable power supply. The present invention also concerns a method for attaching a resistor to a carrier.
2. Background Information
EP 0 522 386 A1 describes an air mass flow meter comprising a film type anemometer with a Venturi tube, which is held in a tubular housing by ribs extending in a radial direction. One of the ribs is hollow and, in a rib recess formed in this fashion, a frame support with two resistors in the form of semiconductor chips projects into the Venturi tube channel. The resistors are held in a bridge-forming position by retaining studs.
In EP 0 522 386 A1, the heat insulation between the resistors and the frame support can be problematic, so that the accuracy when determining the air mass flow can be impaired due to heat transfer from the resistor to the retaining device.
GB-A-22 01 000 discloses a retaining device for a rectangular, plate-shaped, thin-film resistor for an air mass flow meter, which is held by means of elastic steel strips and which is said to have improved heat insulation. The device of GB-A-22 01 000 contains two opposite parallelepiped-shaped retaining elements made of a heat-insulating material and having obliquely extending, V-shaped grooves for engaging the corners of a resistor. The device of GB-A-22 01 000 is a relatively elaborate construction.
DE-PS 31 27 097 discloses a device for retaining plate-shaped, electrical thin-layer resistors consisting of a thin metal layer made from an electrically insulating carrier. The heatable thin-layer resistor bears upon at least three pointed supports of a retaining clamp and is pressed against the supports by at least two brackets of a retaining clamp which are provided with points. DE-PS 31 27 097 aims to meet the objective of providing a device for retaining plate-shaped, electrical thin-layer resistors consisting of a thin metal layer on an electrically insulating carrier, in particular for use in for an anemometer of the film type for measuring flow. The goals of the device of DE-PS 31 27 097 are to provide an accurate and secure positioning in all three dimensions, to ensure an extremely rapid adjustment of the thermal balance and be only negligibly affected by the amount of heat carried-off by the fluid flow of heated thin-layer resistors.
The relatively elaborate construction of DE-PS 31 27 097, according to which the thin-layer resistor is attached at its four corners to four points of a support by means of brackets, so that additional tongues are required for fastening purposes and contact, is problematic.
U.S. Pat. No. 4,320,655 describes a mass flow meter based on a heat-resistance anemometer, whereby not only a heating resistor, but also a comparator resistor, are attached to an electrically insulating carrier using the thin-layer technique. The comparator resistor is applied in a meandering or wavy form.
In U.S. Pat. No. 4,320,655, the relatively large heat capacity of the carrier and the resistor attached thereto, which results in the response properties being relatively slow vis-a-vis fast flow changes, likewise proves problematic.
DE 41 22 295 A1 is directed to an air mass flow meter for the air intake of an internal-combustion engine. DE 41 22 295 A1 describes a device having a tubular housing with a Venturi tube, which is located in a section of the air intake. A first resistor is disposed in the Venturi tube. The temperature and/or resistance of the first resistor is controlled by an electrical circuit, whereby the manipulated variable is the measurement unit for the mass. A second temperature-dependent resistor is provided for compensating the temperature and is longitudinally arranged in the Venturi tube. The first resistor is designed as a bridge in a frame-forming recess of a section of a chip carrier projecting into the Venturi-tube channel. A U-shaped recess is located upstream or downstream in the frame-forming recess over which the second resistor projects as a bridge. In such an arrangement, the heat insulation of the resistor with respect to the retaining device or periphery surrounding it, respectively, is problematic.
Furthermore, resistance thermometers with a substrate consisting of glass or ceramics, in particular in the form of a platelet or a small plate, are known, onto which a thin layer of metal, such as, for example, platinum or nickel, are applied by means of high-vacuum evaporation or cathodic sputtering.